Percutaneous Transluminal Angioplasty (PTA) is a medical procedure for widening a stenosis or constriction of a bodily passage. The most common application is to widen the passage of a blood vessel, such as an artery, which has been constricted by the build-up of cholesterol fats or atherosclerotic plaque. When this medical procedure is applied to a coronary artery, it is referred to as Percutaneous Transluminal Coronary Angioplasty (PTCA).
Typically, a tip mounted balloon of a balloon catheter is advanced over a guidewire to the stenosis. Once the balloon catheter is properly position, the balloon is inflated to compress the plaque against the vessel walls and widen the stenosis. Problems occur, however, when the dilatation of the occlusion forms fissures, flaps and/or dissections which may ultimately cause reclosure or restenosis of the vessel.
To maintain vessel patency and/or strengthen the area undergoing angioplasty or other treatment, an intravascular prosthesis may be employed. These devices are usually introduced percutaneously, transported transluminally and positioned at a desired location within the widened stenosis of the patient. Once properly deployed, the implanted intravascular prosthesis essentially functions as a permanent scaffold for the widened stenosis to reduce the chance of restenosis.
One form of an intravascular prosthesis is a self-expanding stent device which is capable of self-expansion to its proper implantation size after deployment at the site of the stenosis. Usually, these stent devices either self-expand due to exposure to environmental factors (usually the application of body heat), and/or are radially constrained in a compressed condition by a deployment device until released. In the latter design, upon proper positioning and removal of the peripheral constraint, such as a sheath, the self-expanding stent reverts to its expanded state. Self-expanding stents of this nature are generally composed of shape memory alloys or the like such as nitinol which are configured to have a transition temperature just below the normal body temperature. Typical of these self-expanding stents is disclosed in U.S. Pat. No. 4,655,771.
More recently, however, these conventional self-expanding stents (as well as balloon expandable stents) have been embedded or implanted with radioisotopes which they emit predictable amounts of radiation into the widened vessel and immediate surrounding area. It has been found that the proper dosages of radiation reduces tissue regrowth, an effect which is highly beneficial in preventing restenosis of the vessel. Such radioisotope stents are disclosed in U.S. Pat. Nos.: 5,059,166 and 5,176,617, incorporated by reference herein in their entirety.
Although these radioactive stents only emit relatively low levels of radiation, direct contact with the stent by physicians, laboratory technicians, and other personnel should be avoided. As a result, special handling and storage protocols for these radioactive stents must be exercised to minimize radiation exposure. For example, shielding devices have been developed to enable the safe transportation and handling of these radioactive stents and/or the associated stent delivery catheters. Such shield devices are disclosed in U.S. Pat. No. 5,605,530, entitled "System for Safe Implantation of Radioisotope Stents", which is incorporated by reference in its entirety.
Similarly, to transport and deploy these self-expanding radioactive stents, special deployment catheters are applied which have distal tubes containing the compressed stents therein. Once the distal tube is properly advanced and situated at the widened stenosis or the like, the stent is forced from the tube whereupon the stent self-expands to the expanded state. Examples of these deployment devices may be found in U.S. Pat. Nos.: 5,026,377; 4,768,507 and 4,732,152.
The primary problem associated with these deployment devices, however, is that the self-expanding stents (both radioactive and non-radioactive stents) must be compressed before being installed in the distal tube of the deployment device. In some instances, on-site manual compression may be performed by the physician in the catheter laboratory. This process enables the physician to "feel" the compression and to determine the load quality in the delivery tube. The proper compression technique for a self-expanding stent, however, is extremely difficult to perform, and is generally acquired only through substantial practice and experience. A variety of subjective conditions, such as too great or too little compression pressure, may affect the structural integrity and irreparably damage stent. Damage may also occur during loading of the compressed stent into the delivery tube. Moreover, when radioactive stents are applied, direct handling thereof by the physician should generally be avoided altogether.
More preferably, these radioactive self-expanding stents are precompressed for storage in associated deployment devices or catheters at the time of production by the manufacturer. While this loading technique more uniformly controls the loading quality of the compressed stents, a large inventory of self-expanding stent-bearing deployment catheters must be maintained to accommodate the variety of stent types, diameters and stent lengths for each type of delivery catheter. Thus, maintaining such an inventory is not only difficult, but can be very expensive as well.
Moreover, the storage of radioactive stents in these catheters tends to be problematic since the shelf-life for the radioactive stent is substantially different from that of the deployment catheter, depending upon the isotope half-life (e.g., a beta or gamma isotope). For example, the shelf-life for a radioactive stent may range from about 3 days to about 100 days; while that of the deployment device may be about 3 years. This disparity again increases the difficulty of inventory maintenance.
Therefore, it would be highly desirable to uniformly load a self-expanding radioactive stent into deployment device on-site at the catheter laboratory or the like, without requiring the physician, laboratory technician or other personnel to directly handle and contact the radioactive stent.